Method of intermediate frequency modulation inside a radio-frequency modulator tube



Dec. 30,1930. 0. SCHRIEVER 1,786,579

METHOD OF INTERMEDIATE FREQUENCY MODULATION INSIDE A RADIO FREQUENCY MODULATOR TUBE Filed Nov. 21, 1928 INVENTOR OTTO scnmevsw.

A ORNEY Patented Dec. 30, 1930 warren STATES, PATENT OFFICE OTTO ECHRIEVER, OF BERLIN, GERMANY, ASSIGNOR TO TELEFUNKE N GESELLSCHAFT FUR DRAHILOSETELEGRAPHIE M. B. 3., OF BERLIN, GERMANY, A CORPORATION or GERMANY METHOD OF INTERMEDIATE FREQUENCY MODULATION TNSIDE A RADIO-FREQUENCY I MODULATOR TUBE Application filed November 21, 1928. Serial No. 320,827.

In picture telegraphy as well as in highspeed telegraphy it is of great practical advantage to have recourse to an intermediate frequency carrier wave for multiple utilization of a keying cable, said intermediate fre quency or transfer frequency in turn being modulated by the picture point or unit frequency or the keying frequency.

In order to obtain favorable transmitting conditions in long distance work itis quite often and in fact sometimes imperative to establish the transmitting station at a point remote from the studio. Under these conditions one method of conveying the energy to the transmitting point is by means of telephony wires or power lines. In tonal frequencies where the extremes are comparatively small the line constants do not materially affect the energy. However, in picture work where the extremes are sometimes relatively large it can readily be seen that line constants play an important part in transmission work.

The present invention overcomes this drawback by employing an intermediate fre. quency which is modulated by the picture. transmitter. This intermediate frequency is chosen of such a value that when modulated by the picture transmitter the extreme Now, in order that the radio frequency band which is radiated off may not he unnecessarily enlarged, it is desirable to eliminate the said carrier frequency again before modulation of the radio frequency transmitter occurs. This end is attained by demodulation and subsequent filtering out of the intermediate frequency wave by the aid of a rectifier tube.

The purpose of the present invention is to obviate the necessity of providing a separate rectifier tube by reason that the modulator tube of the radio frequency transmitter is utilized at the same time as the demodulator for the intermediate frequency.

Another object of the invention is to provide an improved method of line transmission for picture transmission. Further objects of the invention willappear from the following matter when read in connection with the drawings in which Figure 1 represents one embodiment of my invention in which a filtering system is pro-- vided, and V Figure 2 shows another embodiment utilizing two modulator tubes.

. The circuit arrangement shown in Figure 1 isv the so-called Schaefier direct current grid modulation method and circuit for a valve transmitter. Suppose the transmitter tube 1 is fed with the radio frequency current by'way of transformer T1, while the audio frequency current, in this case the modulated intermediate or transfer frequency is supplied by way of transformer T2 to the modulator tube H. V The basic feature of the invention, as will be noted, consists in that the modulating tube is caused to act as a rectifier by suitable grid biasing potential, while at the plate end a filter circuit (S) is connected which is so proportioned that the carrier current is rendered inefiective thereby, with the result that only the telegraphing signals are allowed to pass to th transmitter valve.

Figure 2 covers the same object, as above described, except that in Fig, 2 means are SliQWYD in which both halves of the intermediate or transfer frequency are utilized for the control of the transmitter. This feature of the invention is realized by having two modulator tubes connected in parallel at the plate end, whereas at the grid end they are operated in phaseopposition. In Figure 2 like letters and like characters are used to describe like parts of the circuits and apparatus. The application of the circuit shown in Figure 2 is self evident since as shown points O() of Figure 2 correspond to points O 0 of Figure 1 and points XX of Figure 2 correspond to the points XX of Figure 1.

The method here disclosed is not confined to grid direct current modulation, but is useful for any other desired tube modulation arrangement.

Having thus described my inventionwhat I desire to protect by Letters Patent is as foll ws;

1. In a signal transmission system, a transmitter tube circuit including means for gene 'ating a carrier wave for the signals to be transmitted, a modulator tube circuit, and a source of intermediate frequency energy, means for modulating said intermediate frequency energy in accordance with signals desired. to be transmitted means for impressing said modulated intermediate frequency energy on said modulator tube circuit, means comprising the modulator tube for demodulating said energy, means comprising said modulating tube for modulating said carrier wave with said demodulated energy and means intermediate said'transmitted tube circuit and said modulator tube circuit for pre venting said intermediate frequency energy from being: impressed upon said transmitter tube circuit.

2. In a signal transmission system, a transmitter tube circuit comprising a transmitter tube and means for generating a carrier wave for the signals to be transmitted, means for modulating said carrier wave comprising a modulator tube circuit, a source of intermediate frequency energy, means for modulat ing said intermediate frequency energy in accordance with signals desired to be transmitted means for impressing; said modulated intermediate frequency energy on said n1odulator tube circuit, means in said modulator tube circuit for demodulating said energy, modulating said carrier waveiwith said demodulated energy and means intermediate said transmitter tube circuit and said modulator tube circuit comprising a filter circuitior preventing said intermediate frequency energy from being impressed upon said transmitter tube circuit.

3. In a signal transmission system, a transmitter tube circuit including means :for generating a carrier wave for the signals to be transmitted, a modulator tube circuit comprising a pair of spaceidischarge devices having their outputs in parallel and their inputs arranged in phase opposition, and a source of intermediate frequency energy, means for modulating said intermediate frequency energy in accordance with signals desired to be transmitted,means for impressing said modulated intermediate frequency energy on said modulator tube circuit, means comprising the modulator tube circuit for demodulating said energy, means comprising said modulating tube circuit for modulating said carrier wave with said demodulated energy and means intermediate said transmitter tube circuit and said modulator tube circuit for preventing any of said intermediate frequency energy from being impressed upon said transmitter tube circuit.

4. Ina signal transmission system, a transmitter tube circuit including means for generating a carrier wave for the signals to be transmitted, a modulator tube circuit comprising a pair of space discharge devices having their output circuits in parallel and their input circuits arranged in phase opposition, and a source of intermediate frequency en ergy, means for modulating said intermediate frequency energy in accordance with signals desired to be transmitted means for impressing said modulated intermediate frequency energy on said modulator tube circuit, means comprising said space discharge devices for demodulating said energy, means comprising said space discharge devices for modulating said carrier wave with said demodulated energy and means comprising a filter circuit intermediate said transmitter tube circuit and said modulator tube circuit for preventing any of said intermediate frequency energy from being impressed upon said transmitter tube circuit.

OTTO SGHRIEVER. 

